Manufacturing methods to shear liquid crystal

ABSTRACT

As a liquid crystal display is assembled, the compressive force of a member or multiple members shears the liquid crystal layer, causing the liquid crystal layer to assume a more uniform, more ordered texture. This novel shearing, coupled with optimal temperature, optimal forms of electromagnetic radiation, and novel combinations of materials synergistically produces a display that is driven at less than 5 volts.

BACKGROUND Prior Art

The following is a tabulation of some prior art that presently appears relevant:

U.S. Patents Patent Number Issue Date Patentee 6,327,017 2001 Dec. 4 Barberi, et al. 5,332,521 1994 Jul. 26 Yuasa, et al. 5,315,419 1994 May 24 Saupe, et al. 4,890,902 1990 Jan. 2 Doane, et al. 4,813,771 1989 Mar. 21 Handschy, et al. 4,685,771 1987 Aug. 11 West, et al.

Foreign Patent Documents Foreign Doc. Nr. Cntry Code Pub. Dt App or Patentee EP 0311979 A2 US 1989 Apr. 19 Handschy, et al. EP19890113368 JP 1994 May 30 Kimihiro, et al. EP0352637 B1 JP 1990 Jan. 31 Kimihiro, et al.

PUBLICATIONS

-   N. A. Clark and S. T. Langerwall; Appl. Phys. Lett., 36 (1980) 899 -   Effect of external electrical field on phase behavior and morphology     development of polymer dispersed liquid crystal Yang, et al.,     European Polymer Journal, Volume 40, Issue 8, August 2004, Pages     1823-1832 -   Phase equilibria of polymer dispersed liquid crystal systems in the     presence of an external electrical field, Tao Chenf, et al., Journal     of Polymer Science Part B: Polymer Physics, Volume 45, Issue 14,     pages 1898-1906, 15, Jul., 2007 -   STRESSED LIQUID CRYSTALS: PROPERTIES AND APPLICATIONS, Thesis, Kent     State University, Guoqiang Zhang August 2007 -   Holographic PDLC Containing Flourine Segments, Kim et al., Bulletin     of the Chemical Society of Japan, Vol. 81 (2008) No. 6 Ppg 773-777.

When testing the voltage characteristics of a polymer dispersed liquid crystal display (pdlc), it is common to report the T90 voltage of the polymer dispersed liquid crystal display. T90 voltage is the voltage required to achieve 90% transparency of a polymer dispersed liquid crystal optical display.

Prior art, patents, and scientific literature report the T90 voltage amounts of pdlc displays. According to the published work of prior workers, the lowest reported T90 voltages for pdlc displays is about 6.0 volts. Typically the T90 voltages are much higher. Often the T90 voltages of PDLC exceed 40 volts.

6 volts is about 200% to 400% higher than the normal operating voltage parameters for commodity lcd mcu driver chips. The high operating voltage of PDLC is one of the reasons why PDLC has been used mostly for privacy windows.

PDLC workers have experimented with controlling the ambient air temperature surrounding the pdlc device during exposure to ultraviolet light, and the temperature of the pdlc mixture, and the temperature of the entire pdlc device during exposure to ultraviolet light. Few workers have reported a voltage below 6 volts.

PDLC workers have experimented with electrically annealing the pdlc display during exposure to ultraviolet radiation. Few workers have reported a voltage below 6 volts.

PDLC workers have experimented with adding fluorinated acrylate resins to the pdlc mixture. Few have reported a voltage below 6 volts.

Liquid crystal workers have experimented with a variety of shearing techniques to optimize displays.

To align lyotropic liquid crystals, it is known in the art to coat the lyotropic mixture onto the bottom substrate, and then directly contact the lyotropic mixture with a doctor blade to shear the lyotropic mixture. Then the top substrate is attached to the bottom substrate.

It is also known in the art to shear liquid crystal which is dispensed between 2 rigid substrates. The rigid substrates that comprise the the liquid crystal cell are pulled in opposite directions, which causes a shearing force on the liquid crystal layer. (N. A. Clark and S. T. Langerwall; Appl. Phys. Lett., 36 (1980) 899). Their technique can only be scaled up to a batch process, not a continuous process.

To shear ferroelectric displays, it is known in the art to gently shear the display laminate around rubber rollers. As the films comprising the laminate are handled around a round roller, the respective justaposed display substrates are stretched at different speeds, shearing the ferroelectric mixture distributed between the two substrates. The shear force exerted on the ferroelectric layer by the films having different stretching speeds is relatively small, not comparable to the shearing force of a doctor blade on a liquid crystal layer.

In his thesis Zhang teaches “In addition to variation of monomer categories and compositions, mechanical modifications are also applied to liquid crystal/polymer composites, introducing unique properties, such as alignment of liquid crystals, [42], [43] macroscopic birefringence, [44] and improved electro-optical performance. [45]”

“There are mainly three types of mechanical deformation applied to the liquid crystal/polymer composites: (1) shear deformation; (2) stretch deformation; and (3) compress deformation.”

Wu et al. [45] have demonstrated that shear force can produce alignment to liquid crystal droplets inside PDLCs and improve response speed. Amundson et al. [44] find that sheared PDLC samples of high liquid crystal concentration (˜80 wt %) exhibit large birefringence due to the uniform alignment of liquid crystals induced by shear force. Other groups have used shear stress during the phase separation process to align liquid crystals in many liquid crystal polymer composite systems. For instance, Sixou et al. [46-48] build sheared polymer dispersed nematic liquid crystals (PDNLC) and sheared polymer dispersed cholesteric liquid crystals (PDCLC) and demonstrate the elliptical shape of liquid crystal droplets formed by the shear using scanning electron microscopy. The characterized electro-optical performance of the PDNLC is consistent with the theoretical prediction. Sheared PDCLC shows a correlation between ellipticity and reflectivity: larger ellipticity produces blue-shifted and narrower reflection band. Kitzerow et al. [49,50] successfully achieve prealignment for ferroelectric liquid crystals inside a polymer matrix by applying shear force during polymerization, avoiding the difficulty of building surface stabilized ferroelectric liquid crystal devices of which the cell gap is usually thinner than 2 μm.”

In general, liquid crystal displays are manufactured using batch processes. Batch processes are usually slower than continuous, roll to roll manufacturing processes.

Currently polymer dispersed liquid crystal displays are driven by electronic circuits which have higher voltages than many twisted nematic displays or super twisted nematic displays.

U.S. Pat. No. 4,094,058 Yasutake et al. 1978-6-13 describes manufacturing a liquid crystal display. The device described in this patent would not function without at least a polarizer or other similar optical component. Polarizers are required for all electrically driven liquid crystal displays: dynamic scattering mode, twisted nematic, super twisted nematic—all require polarizers. Polymer dispersed liquid crystal displays and cholesteric liquid crystal displays became patent many years after the claims of U.S. Pat. No. 4,094,058. The display device described in U.S. Pat. No. 4,094,058 does not describe any device which functions as a display.

U.S. Pat. No. 4,924,243 Sato, et al. 1990-5-8 describes a method for forming spacers by printing.

The patent describes a resin which shrinks from 20 microns to 2+−0.5 microns. There are few resins known, certainly no epoxy adhesives, that do not contain solvent or air which can shrink 90%. Claim 5 states that the resin is an epoxy adhesive.

The patent does not state how the (tacky) adhesive releases from the scratched cylinder. The patent does not consider that it is not common for a gravure cylinder to release 100% of each gravure cell's contents, especially when the objective is to lay down a coating 20 microns thick.

The patent does not consider that there is no known squeegee and gravure cylinder assembly wherein 100% of the adhesive remaining on the outer surface of the cylinder (the unengraved “land” area) is removed. Usually a minute amount of residual ink is transferred to the surface being printed. The remaining ink coating is so thin that it is transparent to the human eye. However, even a minute thickness coating can have dramatic results for the performance of a liquid crystal display. In particular ferroelectric displays are known to be readily distorted by minute surface disturbances.

The patent claims a “printing roll engaged with said cylinder which receives said material . . . and transfers . . . to a surface of said substrate” Doing so is very problematic. The surface characteristics of the printing roll engaged are not the same as the surface characteristics of the substrate. To claim that an uncured epoxy adhesive 20 microns thick will transfer completely from the hard scratched cells of the cylinder to the surface of the printing roll engaged, and then transfer completely from the printing roll to the substrate is problematic.

In addition, the display requires baking at 150 C for an hour, which exceeds the usage temperatures of commodity polymer substrates.

U.S. Pat. No. 4,228,574 Culley et al. 1980-10-21 describe a roll to roll continuous process of manufacturing (twisted nematic) liquid crystal displays. A full critique of U.S. Pat. No. 4,228,574 is outside the purpose of this document, so I will highlight a few of the many improbabilities described in U.S. Pat. No. 4,228,574.

-   -   (1) In U.S. Pat. No. 4,228,574 A polarizer is attached to a         birefringent mylar film. This is improbable, because the         birefringent films listed in the patent would distort the         function of the polarizer.     -   (2) In U.S. Pat. No. 4,228,574 the transparent conductor indium         tin oxide would likely develop shorts as it is handled by the         numerous stations downstream from the indium tin oxide         application station.     -   (3) In U.S. Pat. No. 4,228,574 applying a photoresist film and         patterning a photoresist film usually requires an intermittently         moving production line, to allow for exposure of the         photoresist, and the removal of the resist in multiple liquid         chemical baths. But many of the other stations described in the         patent require a continuously moving production line.     -   (4) In U.S. Pat. No. 4,228,574 rubbing direction is critical to         the functioning of liquid crystal displays. To optimize the         rubbing, the polarizer orientation and the rubbing direction         cannot both be parallel to the moving machine direction of the         web, nor both parallel to the transverse machine direction. The         patent does not adequately describe the means to rub the carrier         substrate continuously.     -   (5) In U.S. Pat. No. 4,228,574 Liquid crystal material with         fiber spacers is introduced between the top and bottom films.         The patent does not indicate the means whereby the liquid         crystal material and fiber spacers are introduced, and the means         of doing so on a continuous production line is not trivial.     -   (6) In U.S. Pat. No. 4,228,574 Conductive epoxy is introduced         between the top film and the bottom film. Epoxy, polymerized by         heat and catalyst, is another example of a process station that         is intermittent, and curing of the catalyst requires significant         dwell time.     -   (7) If U.S. Pat. No. 4,228,574 were efficient, the assignee         would likely have commercialized the processes during the past         35 years.         -   I consider U.S. Pat. No. 4,228,574 to contain many             improbable processes.

U.S. Pat. No. 4,924,243 1990-5-8 Sato et al. describes a thermoset epoxy resin which requires significant dwell time to polymerize.

Advantages

Accordingly several advantages of one or more aspects are as follows: the synergism of the manufacturing techniques optimizes the morphology of the polymer dispersed liquid crystal mixture so that the mixture has a T90 of 6 volts or less, and so can be driven by commodity grade semiconductors, and the substrates and the chemicals thereinbetween can be laminated with roll to roll equipment, continuously, at production speeds much faster than batch processes.

Other advantages of one or more aspects will be apparent from a consideration of the drawings and ensuing description.

DRAWINGS FIGS. 1-3

FIG. 1 shows a single doctor blade which laminates and/or shears the liquid crystal display

FIG. 2 shows two doctor blades which laminate and/or shear the liquid crystal display.

FIG. 3 shows two sets of two doctor blades which laminate and/or shear the liquid crystal display

DETAILED DESCRIPTION FIGS. 1-3

Referring to FIG. 1, roller 126 and roller 128 support the bottom surface 110 of plastic film or continuous web or plastic film sheet or metalized film or bottom substrate 112. Liquid crystal layer 116 is deposited or printed or coated or jetted or cast onto the top surface 114 of bottom substrate 112. Bottom surface 118 of plastic film or continuous web or plastic film sheet or metalized film or top substrate 120 is in contact with liquid crystal layer 116. Doctor blade or ductor blade 124 is in contact with the top surface 122 of the top substrate 120. The doctor blade 124 compresses the top substrate 120, causing the liquid crystal layer 116 to shear. Roller 130 contacts the top surface 122 of the top substrate 120. Roller 130 is in vertical alignment with roller 128.

Referring to FIG. 2, roller 226 and roller 228 support the bottom surface 210 of plastic film or continuous web or plastic film sheet or metalized film or bottom substrate 212. Liquid crystal layer 216 is deposited or printed or coated or jetted or cast onto the top surface 214 of bottom substrate 212. Bottom surface 218 of plastic film or continuous web or plastic film sheet or metalized film or top substrate 220 is in contact with liquid crystal layer 216. Doctor blade or ductor blade 224 is in contact with the top surface 222 of the top substrate 220. Doctor blade or ductor blade 232 is in contact with the bottom surface 210 of the bottom substrate 212. Doctor blade 224 is in vertical alignment with doctor blade 232. Doctor blade 224 compresses the top substrate 220, while doctor blade 232 simultaneously compresses the bottom substrate 214, causing the liquid crystal layer 216 to shear. Roller 230 contacts the top surface 222 of the top substrate 220. Roller 230 is in vertical alignment with roller 228.

Referring to FIG. 3, roller 326 and roller 328 support the bottom surface 310 of plastic film or continuous web or plastic film sheet or metalized film or bottom substrate 312. Liquid crystal layer 316 is deposited or printed or coated or jetted or cast onto the top surface 314 of bottom substrate 312. Bottom surface 318 of plastic film or continuous web or plastic film sheet or metalized film or top substrate 320 is in contact with liquid crystal layer 316. Doctor blade or ductor blade 324 is in contact with the top surface 322 of the top substrate 320. Doctor blade or ductor blade 332 is in contact with the bottom surface 310 of the bottom substrate 312. Doctor blade 324 is in vertical alignment with doctor blade 332. Doctor blade 324 compresses the top substrate 320, while doctor blade 332 simultaneously compresses the bottom substrate 312, causing the liquid crystal layer 316 to shear. Doctor blade or ductor blade 334 is in contact with the top surface 322 of the top substrate 320. Doctor blade or ductor blade 336 is in contact with the bottom surface 310 of bottom substrate 312. Doctor blade 334 is not in vertical alignment with doctor blade 336. Doctor blade 334 compresses top substrate 320, while doctor blade 336 simultaneously compresses bottom substrate 312, causing the liquid crystal layer 316 to shear. Roller 330 contacts the top surface 322 of the top substrate 320. Roller 330 is in vertical alignment with roller 328.

Some embodiments provide a method of producing a liquid crystal optical device, which methods comprise, in sequence, providing a layer of a liquid crystal composition on the electrode layer of a substrate carrying electrode layer, laminating and shearing an opposite substrate carrying electrode layer on the substrate carrying electrode layer which has been provided, on its electrode layer, with the layer of the liquid crystal composition, so that the layer of the liquid crystal composition lies between the electrode layers, to obtain a liquid crystal optical device yet to be laminated and sheared, laminating and shearing the liquid crystal composition enclosed in the liquid crystal optical device yet to be laminated and sheared.

Other embodiments provide a method of producing a liquid crystal optical device, which methods comprise, in sequence, providing a layer of a liquid crystal composition comprising a polymer dispersed liquid crystal material and a resin having crosslinking ability on the electrode layer of a substrate carrying electrode layer, laminating and shearing an opposite substrate carrying electrode layer on the substrate carrying electrode layer which has been provided, on its electrode layer, with the layer of the polymer dispersed liquid crystal composition, so that the layer of the polymer dispersed liquid crystal composition lies between the electrode layers, to obtain a liquid crystal optical device yet to be laminated and sheared, laminating and shearing the polymer dispersed liquid crystal composition enclosed in the liquid crystal optical device yet to be oriented, and crosslinking the resin having crosslinking ability enclosed in the oriented liquid crystal optical device.

Other embodiments employ a method continuous and high-speed mass production method wherein a layer of a polymer dispersed liquid crystal composition is formed by continuously applying the composition on a flexible plastic substrate bearing substrate by using the above-described application technique or the like, during moving the substrate at a high speed and then, an opposite plastic substrate carrying electrode layer is layered on the layer of the liquid crystal composition and continuously laminated and sheared.

The orienting treatment is continued past the nips of the laminating and shearing devices. Orienting is maintained by thermal annealing and electrical annealing after formation of film and lamination and shearing.

Another embodiment comprises a method of orienting the polymer dispensed liquid crystal composition of the present invention is to orient the polymer dispersed liquid crystals in a liquid crystal optical device produced as described above by subjecting the liquid crystal optical device yet to be oriented to a shearing treatment by a doctor blade or other tool.

The PDLC laminate is handled around 1 or more doctor blades. Preferably the PDLC laminate is handled by at least 2 doctor blades. Each doctor blade compresses the outside surface of one of the substrate films, causing the PDLC mixture deposited therein to also compress. As the film moves past the doctor blade nip, the PDCL then decompresses. The compression and decompression forces shear the PDLC mixture, forming the liquid crystal mixture into a uniform texture.

As said PDLC laminate has been handled by one doctor blade, it can also be simultaneously handled by another doctor blade, or by another doctor blade downstream of the first doctor blade. The opposite doctor Blade affects the outside surface of the substrate which previously was not contacted by a doctor blade. This opposite doctor blade compresses the outside surface of one of the opposite substrate film, causing the PDLC mixture deposited therein to also compress. As the film moves past the doctor blade nip, the PDLC then decompresses. The compression and decompression forces shear the PDLC mixture, further forming the liquid crystal mixture into a uniform texture.

In some embodiments, in order to attain a uniform orientation in the whole liquid crystal cell, the shearing treatment is conducted during the continuous moving of the web past the doctor blades.

In some embodiments, the above-described orientation by shearing treatment can be conducted by using various kinds of apparatuses and systems, such as rollers, bristles, felt pads, doctor blades, and others.

In still other embodiments, orientation of liquid crystals by means of the above-described shearing treatment can be performed more effectively and more efficiently by subjecting a liquid crystal optical device to the shearing treatment in the course of continuous movement of the liquid crystal optical device. Particularly, it can be performed furthermore effectively at a speed equal to the UV curing speed of the pdlc laminate as it is cured past several uv sources, enabling mass production, by continuously moving and handling the liquid crystal optical device past multiple doctor blades that shear the liquid crystal.

The moving speed of the liquid crystal optical device during the shearing treatment cannot be uniformly defined because it varies depending on the speed of the pdlc laminate as it is cured by multiple uv sources, the ambient temperature, the kinds of the liquid crystals used, etc. It is generally sufficient to adjust the speed to the line speed of a continuous production process. Therefore, it is possible to equalize all of the line speeds in various steps including the orientation step by shearing treatment, whereby a continuous, high-speed process for mass producing liquid crystal optical devices can be efficiently realized, resulting in an extreme improvement of mass productivity.

We have discovered a synergism between the following pdlc manufacturing techniques: the ambient temperature of curing, the temperature of the pdlc mixture and that of the device itself, the electrical annealing, the duration and intensity of the ultraviolet light exposure, the addition of fluorinated acrylates, and shearing around multiple doctor blades. This synergism fabricates a pdlc display with a T90 under 4.5 volts.

Here is a simplified description of one embodiment of the manufacturing steps:

The pdlc liquid crystal mixture is disposed between the polymer film substrates, and the substrates are adhered together to form a laminate,

Before curing the polymer dispersed liquid crystal mixture, the pdlc film laminate comes into contact with one to several doctor blades. If multiple doctor blades are used, it may be efficient to position the doctor blades opposite each other on alternating sides of the film laminate. As the film laminate comes into abrupt contact with the sharp edge of the doctor blade, the film is dramatically and significantly compressed. The abrupt compressive force of the doctor blade, followed by the relaxing of the pdlc mixture, shears and orients the liquid crystal mixture. The shearing causes a uniform polymer dispersed order, which remains uniform as the pdlc mixture is cured by ultraviolet light.

Tools effective at laminating and shearing the display are doctor blade or blades, or rollers, or a myriad of hairs, or a myriad of fibers, or a myriad of filaments, or wipers. These devices gently bring the two substrates together.

The pdlc film laminate is cured by ultraviolet light, within a specific temperature range to optimize the morphology of the polymer dispersed liquid crystal mixture.

The pdlc mixture is affected by an AC electrical wave of about 100 Hz, and a voltage of about 20 volts.

Common liquid crystal mixtures are polymer dispersed liquid crystals, guest host liquid crystal mixtures, nematic liquid crystals, ferroelectric liquid crystals, super twisted nematic liquid crystals, and cholesteric liquid crystal mixtures.

It is known that free radical polymers polymerize when affected by radiation like ultraviolet radiation, electron beam radiation, laser radiation, near-visible radiation, or visible light radiation.

Kim et al. teaches “Addition of fluorinated monomer gave long saturation time, increased off state diffraction efficiency, small anchoring strength and driving voltage.” Some of the embodiments comprise 2-(perfluoroalkyl)ethyl methacrylate (PFEMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), and 2,2,2-trifluoroethyl acrylate (TFEA).

This shearing action discussed above, in syngergism with the curing techniques discussed above, fabricates a pdlc display with T90 under 4.5 volts. 

What is claimed is: 1) A method for continuously manufacturing and ordering a liquid crystal optical device yet to be ordered which comprises: (a) providing two flexible substrates that are parallel to each other, (b) said flexible substrates having surfaces facing each other on which are disposed respective electrode layers, (c) and one substrate supports a layer of a liquid crystal composition, (d) bringing said substrates together into a nip, combining within said nip said substrates into a laminate, (e) further handling the laminate by a member with a means to exert a predetermined compressive force upon said laminate, by contacting the exterior surfaces of said laminate, so that said liquid crystal layer deposited within said laminate is sheared and thereby becomes ordered, (f) polymerizing the resins within said liquid crystal layer with electromagnetic radiation, and (g) cutting said laminate into a plurality of separate liquid crystal displays.
 2. The liquid crystal optical device of claim 1, wherein the radiation is selected from the group comprising ultraviolet radiation, electron beam radiation, laser radiation, near-visible radiation, or visible light radiation.
 3. The liquid crystal composition of claim 1, wherein the liquid crystal composition is selected from the group comprising polymer dispersed liquid crystal mixtures, guest host liquid crystal mixtures, nematic liquid crystals, ferroelectric liquid crystals, super twisted nematic liquid crystals, and cholesteric liquid crystal mixtures.
 4. The shearing treatment of claim 1, performed by a member selected from the group of doctor blades, doctor rollers, brush fibers, filaments, or wipers.
 5. The method of producing a liquid crystal optical device as claimed in claim 1, wherein the polymerization of the polymers comprising the polymer dispersed liquid crystal mixture is performed at a predetermined temperature range.
 6. The method of manufacturing a liquid crystal optical device in claim 1, wherein the polymerization of the liquid crystal mixture occurs simultaneously as the liquid crystal device electrodes are energized with an alternating current of a predetermined voltage value and voltage frequency.
 7. The liquid crystal optical device of claim 1 wherein the device, when energized, achieves a transparency of 90% at less than 10 volts.
 8. The liquid crystal composition of claim 1 wherein the resin mixture comprises at least one kind of flourinated acrylate.
 9. The liquid crystal composition of claim 1, wherein the the fluorinated acrylate is selected from the group comprising 2-(perfluoroalkyl)ethyl methacrylate (PFEMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), or 2,2,2-trifluoroethyl acrylate (TFEA). 